1. Technical Field
The present invention relates to a bidirectional 3 phase power meter for compensating reverse load flow and a method for metering thereby.
2. Background
Problems metering excessively or insufficiently have been caused due to a reverse load flow phenomenon in a power provider's system, regardless of used power by a user or generated power.
Here, the reverse load flow refers to a energy that flows from the load side to the source side, and is a ground source supplied through the neutral line in a Yg-Δ connection type. Generally, no reverse load flow occurs in a Δ-Y connection type a receiving transformer, but the Yg-Δ connection type is a common connection of an interconnection transformer of DGs(Distributed Power Generation).
Especially, such a reverse load flow phenomenon severely occurs in a transmission and distribution power system interconnected with distributed power occurrence such as photovoltaic power occurrence, wind power occurrence and the like, which causes an error therefore, regardless of accuracy of a power meter.
A power meter calculates the price based on maximum power, active power usage, and power factor. A calculation zone of a power meter is the region where a reactive power region is overlapping to an active power region.
In the reactive power region, there are various kinds of var-hour (reactive power) meters as 0 to 180° region is a lagging reactive power zone, 60 to −120° region is a lagging and leading reactive power zone, and 90 to −90° region is a lagging and leading zone. For example, a reactive power meter of the lagging zone of 0 to 180° does not meter the leading reactive power. However, the leading reactive power is metered during the power transmission and this causes an error when power factor is calculated. In the 60 to −120° region, the leading power and the lagging power are metered at the same time but the region above 60° cannot be metered. Therefore, it is the most apparent that the active power region and the reactive power region be overlapped as in the calculating zone.
In general, a power receiving consumer uses Δ-Y wiring method for an interconnection transformer and a power transmitting consumer uses Yg-Δ wiring method. A general load flow direction of a power receiving consumer is the direction from a power provider to a power user and a load flow direction of a power transmitting consumer is the direction from a power user to a power provider. When load flow per phase, unlike identical 3 phase load flow, is mixed in a direction from a power supply side to a load side or from a load side to a power supply side, a measurement error may occure because load unbalance in a power system occurs due to a wiring method of the interconnection transformer and a load flow direction of one phase among 3 phases is thus changed which is called as reverse load flow. This problem usually occurs in the power transmitting side but it sometimes occurs in the power receiving side due to a wiring system of the interconnection transformer.
A conventional power transmitting side installs a power receiving power meter and a power transmitting power meter and calculates amount of power receiving power and amount of power transmitting power, respectively. Here, in the power receiving state, a power receiving power meter operates and in the power transmitting state, a power transmitting power meter operates. However, in the reverse load flow state, since a reverse load flow is occurred in a power provider's system, a power receiving power meter and a power transmitting power meter cause extremes errors.
The power transmitting power meter has identical structure to the power receiving power meter and a bidirectional power meter measuring for both power transmitting and power receiving uses by combining two of a one way metering system.